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Section 8-3 Meiosis

Section 8-3 Meiosis. Obj 9 : List and describe the phases of meiosis. Meiosis I: Preceded by copying of DNA in interphase. Prophase I. Homologous chromosomes pair each pair = tetrad (4 chromatids) Crossing-over may occur

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Section 8-3 Meiosis

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  1. Section 8-3Meiosis

  2. Obj 9: List and describe the phases of meiosis Meiosis I: Preceded by copying of DNA in interphase

  3. Prophase I • Homologous chromosomes pair • each pair = tetrad (4 chromatids) • Crossing-over may occur • Chromatids twist around each other & parts are exchanged (genetic recombination)

  4. Metaphase I • tetrads line up

  5. Anaphase I • chromosomesmove to opposite poles • independent assortment - random separation of chromosomes, resulting in genetic variation

  6. Independent assortment • http://10.20.0.2/videos/pmp/videos/wm/1MB/8VH0457G_1Mb.wmv

  7. Telophase I • chromosomes reach opposite poles • cytokinesis forms 2 cells

  8. Meiosis II Not preceded by copying of DNA • Occurs in both cells • Same 4 phases - prophase II, metaphase II, etc.

  9. Meiosis II Difference: • In anaphase II, chromatids separate (not chromosomes)

  10. Obj 10: Compare the products of mitosis with those of meiosis • Both from a 2n parent cell: • Mitosis produces 2 diploid (2n) daughter cells • Meiosis produces 4 haploid (1n) gametes

  11. Meiosis

  12. Obj 11: Explain crossing-over and how it contributes to the production of unique individuals • During pairing up, chromosomes exchange DNA • results in new (unique) genetic combinations

  13. Obj 12: Summarize the major characteristics of spermatogenesis and oogenesis Spermatogenesis: • Cytoplasm divides evenly and produces 4 haploid cells • Spermatids grow flagella and are oval

  14. Oogenesis: • Cytoplasm divides unevenly • Egg receives majority of cytoplasm • Polar bodies receive little cytoplasm • will die and are absorbed

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